使用文本框和自定义词典进行拼写会降低我在C＃WPF中的应用程序速度

I am using a WPF TextBoxes inside my WinForm application for spell checking. Each time I create one, I load the same file in as a CustomDictionary. All has been fine until recently. Now, they take a long time to load, up to a second. Some forms have 30 or more, meaning delays of nearly half a minute. This seems to be the case Windows 10 (not Windows 8 as I originally posted). The application is running under DotNet 4.0, I have tried 4.5 and 4.6 (not 4.61) and all versions are slow.I am using a WPF TextBoxes inside my WinForm ap